package com.vedeng.study.util;

/**
 * @Description: 雪花算法
 * @author: Thresh.xie
 * @Date: 2021/12/14
 */
public class SnowFlake {

    public static Long generatorId(){
        SnowFlake snowFlake=new SnowFlake(0, 0);
        return snowFlake.nextId();
    }



    /** 起始的时间戳 */
    private final static long START_STMP = 1609430400L;

    /** 序列号占用的位数 */
    private final static long SEQUENCE_BIT = 12;
    /** 机器标识占用的位数 */
    private final static long MACHINE_BIT = 5;
    /** 数据中心占用的位数 */
    private final static long DATACENTER_BIT = 5;

    /** 每一部分的最大值 */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /** 每一部分向左的位移 */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    /** 数据中心 */
    private long datacenterId;
    /** 机器标识 */
    private long machineId;
    /** 序列号 */
    private long sequence = 0L;
    /** 上一次时间戳 */
    private long lastStmp = -1L;

    public SnowFlake(long datacenterId, long machineId) {

        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;
        // TIMESTMP_LEFT    时间戳部分
        // DATACENTER_LEFT  数据中心部分
        // MACHINE_LEFT     机器标识部分
        // sequence         序列号部分
        return (currStmp - START_STMP) << TIMESTMP_LEFT
                | datacenterId << DATACENTER_LEFT
                | machineId << MACHINE_LEFT
                | sequence;
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }


    public static void main(String[] args) {
        //SnowFlakeUtil util=new SnowFlakeUtil();
        SnowFlake snowFlake=new SnowFlake(0, 0);
        for (int i = 0; i < 10; i++) {
            System.out.println();
        }
    }
}
